Torque-Limiting Screw Cap Using Sacrificial Break or Ratchet
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Solution Overview
Problem
Existing tightening screws lack effective mechanisms to prevent excessive tightening, which can lead to damage or over-tightening issues.
Innovation Solution
A torque limiting cap made of plastic or metal, featuring a recess and protrusion that destructs when a predetermined torque is exceeded, or a ratchet mechanism that allows rotation in one direction but blocks in the opposite, to limit applied torque and prevent over-tightening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If no torque limiting mechanism is used, then the screw can be tightened freely, but excessive tightening may occur causing damage
Solution Approach 1:
The torque limiting function is segmented from the screw body and implemented through a separate cap component. The cap can be attached to or integrated with the screw head, creating a modular torque limiting mechanism that prevents excessive tightening without fundamentally redesigning the entire screw structure.
Solution Approach 2:
The torque limiting cap is designed as a sacrificial component that destructs when the torque limit is exceeded. This disposable element protects the more valuable screw and fastened components by failing first, absorbing the excessive torque through controlled destruction of the cap's torque transferring feature.
2Reliability
If a torque limiting cap is added, then excessive tightening is prevented, but the device complexity increases
Solution Approach 1:
The torque limiting cap is designed to merge with the screw head through various coupling methods including friction fit, interference fit, or positive mechanical engagement features. This integration reduces the number of separate components and simplifies the assembly process, offsetting the added complexity of the torque limiting function.
Solution Approach 2:
The cap structure is designed to serve multiple functions: it provides the torque limiting feature through its destructible torque transferring mechanism, provides a interface for torque application during installation, and can be designed to match various screw head types. This multi-functionality reduces the need for additional specialized components.
3Reliability
If the torque limiting cap is made of plastic, then it can be destructed to limit torque, but the strength may be insufficient for high torque applications
Solution Approach 1:
The material properties of the cap can be varied by changing the plastic type, wall thickness, or geometric parameters of the torque transferring feature. This allows customization of the torque limit to match specific application requirements, enabling the same basic cap design to serve multiple torque ranges through parameter adjustment rather than complete redesign.
Solution Approach 2:
The cap can be constructed from composite materials or material combinations that provide both the necessary strength for the intended torque application and the controlled destructibility at the torque limit. This may include fiber-reinforced plastics or multi-layer constructions that balance strength and sacrificial failure characteristics.
4Ease of operation
If the recess for screw driver is made accessible, then the screw can be untightened, but the torque limiting function might be circumvented
Solution Approach 1:
The torque limiting cap is designed to be removed or destructed as a preliminary step before the screw can be untightened. This sequence ensures that the torque limiting function has been activated (either by normal use exceeding the limit or by intentional removal), and only after this preliminary action can the screw be accessed for loosening, maintaining the integrity of the torque limiting protection.
Solution Approach 2:
Instead of making the screw head directly accessible from the start, the design inverts the access sequence by placing the cap over the screw head. The cap must first be removed or destructed before the screw driver can engage the screw head, reversing the typical access pattern and ensuring torque limiting is respected before loosening operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents excessive tightening by destructing the cap or engaging a ratchet mechanism, allowing for controlled torque application and reusability of the screw.
Implementation Method 1
the torque limiting cap is adapted to be destructed at the recess by the screw driver when the torque applied by a screw driver to the cap exceeds a predetermined value so as to limit the torque to be applied to the screw
Implementation Method 2
the torque transferring feature comprises a ratchet mechanism which allows rotation of the cap relative to the screw head in a tightening direction if the torque applied to the cap exceeds a predetermined threshold value and blocks rotation relative to the screw head in an opposite direction
Data Source
Figure 1~3
Figure 4~7
Figure 8~10
AI summary
A metal tightening screw (17, 27, 37, 7) has a screw head (17A, 27A, 27, 37A, 37, 7A) and a screw shank (7B). The screw shank (7B) is provided with a male thread adapted to cooperate with a female fastening means. A torque limiting cap (19, 29, 39, 9) is arranged on the screw head (17A, 27A, 27, 37A, 37, 7A). The torque limiting cap (19, 29, 39, 9) includes at least one torque transferring feature that couples the cap (19, 29, 39) to the screw head (17A, 27A, 27, 37A, 37, 7A) in a rotational direction. The torque limiting cap (19, 29, 39, 9) may be made of plastic which is adapted to be destructed at a recess (193) by the screw (17, 27, 37) driver when the torque applied by a screw (17, 27, 37) driver to the cap (19, 29, 39) exceeds a predetermined value so as to limit the torque to be applied to the screw (17, 27, 37). The torque limiting cap (19, 29, 39, 9) may also be made of metal which is adapted to be deformed at a recess (193) by the screw (17, 27, 37) driver when the torque applied by a screw (17, 27, 37) driver to the cap (19, 29, 39) exceeds a predetermined value. Another option is that a ratchet mechanism is applied which allows rotation of the cap (19, 29, 39) relative to the screw head (17A, 27A, 27, 37A, 37, 7A) in a tightening direction (20) if the torque applied to the cap (19, 29, 39) exceeds a predetermined threshold value and blocks rotation relative to the screw head (17A, 27A, 27, 37A, 37, 7A) in an opposite direction (21).